1. Field of the Invention
The present invention relates to an image processing technique for controlling a load amount of a color material.
2. Description of the Related Art
In a case where an image is printed by an electronic photograph-type image forming apparatus by printing a straight line image (line image) extending in a (main scanning) direction orthogonal to a conveying direction, a phenomenon may be caused as shown in FIG. 2A in which toner is scattered at a rear side in the conveying (sub scanning) direction of a line image 202 printed on a paper 201. This phenomenon is called a tailing phenomenon (hereinafter referred to as tailing). The tailing is caused, as shown in FIG. 2B, in a case where the paper 201 is rapidly heated while passing through a high-temperature fixing unit 301 to thereby cause the blowout from the paper 201 of the steam 302 of the water in the paper 201. Specifically, the blowout of the steam blows, to the rear side in the conveying direction, developer 303 (also may be called as a color material or toner) on the paper 201 prior to a fixing process.
One technique to suppress the tailing is to subject pixel data to a pattern matching to perform a culling processing on pixels matching a predetermined pattern, thereby reducing the load amount of the developer onto the paper 201 (see Japanese Patent Laid-Open No. 2009-23283). The pixel culling processing is a process to convert black pixels to white pixels or a process to convert colored pixels to colorless pixels. In the case of the electronic photograph-type image forming apparatus, an electronic photograph photoreceptor has thereon a strong electric field (which is called an edge field) formed at an edge rather than the center of an electrostatic latent image. Thus, the toner load amount increases toward the lower end of the edge of the line image in the conveying direction. Thus, more tailing can be effectively suppressed in a case where a culling process is performed on pixels closer to the lower end of the edge of the line image in the conveying direction.
On the other hand, one technique to improve the printing quality of characters and lines is to detect an edge of a character or a line to add black pixels (or to convert white pixels to black pixels) to the neighboring region of the detected edge to thereby expand the edge (line width correction processing) (see Japanese Patent Laid-Open No. 2000-206756).
In a case where a parallel configuration is realized by a tailing suppression processing unit for performing the above-described culling processing for the tailing suppression and a line width correction processing unit for performing a line width correction processing, the respective processings are independently performed to inputted pixel data. In this case, the respective processing units must consider the processings by other processing units otherwise a disadvantage as described below is cause. For example, in a case where a line image is inputted to this parallel configuration, then the respective processing units output pixel data obtained by subjecting the inputted line image to the tailing suppression processing and another pixel data subjected to a line width correction processing for expanding the edge of an inputted line image. Then, by combining these pieces of pixel data, output pixel data is finally generated. In the process of this processing, the tailing suppression processing is performed to determine to-be-culled lines and a culling pattern in the line image based on the width of the inputted line image. On the other hand, the line width correction processing expands the edge region. As a result, the inputted pixels that have originally formed the edge do not form an edge anymore. In such a case, a deteriorated image quality may be caused by a deteriorated tailing suppression effect because an image having passed the image fixing units is an image, which is obtained by the culling processing for the tailing suppression which is performed at a position away from the lower end of the edge in the conveying direction.